JP2003063807A - Method for manufacturing oxygen and method for reforming gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing oxygen capable of manufacturing oxygen at high efficiency by increasing the oxygen permeability of a separation membrane for manufacturing oxygen and a method for reforming gas capable of reforming a gas at high efficiency by raising the oxygen permeable performance of a diaphragm reactor. SOLUTION: Oxygen is manufactured by using, as the separation membrane for manufacturing oxygen, a mixed conductive oxide which contains lanthanum, strontium, cobalt and iron as the main components with molar ratio of the component elements shown in the following formula (1) and which is a dense material having an opening pore ratio of 0.7% or less. The gas is reformed by using such the mixed conductive oxide as the diaphragm reactor. La:Sr:Co: Fe=x:1-x:1-y:y...(1) (where 0<x<0.15, 0<y<0.15).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an oxygen production method using a separation membrane for oxygen production and a gas reforming method using a diaphragm reactor.

[0002]

2. Description of the Related Art Mixed conductive oxides are widely known as substances that selectively transport only oxygen components from an oxygen-containing mixed gas such as air, and such mixed conductive oxides are used in oxygen production equipment. It is used as a separation membrane of the above and a membrane reactor of a gas reformer. Here, the mixed conductive oxide is an oxide that conducts electrons or holes and simultaneously conducts oxygen ions (also referred to as oxide ions).

In order to industrially carry out selective oxygen transport utilizing such a mixed conductive oxide, the oxygen ion conductivity under the operating conditions needs to be about 0.1 S / cm or more, preferably. , 0.5 S / cm or more, and most preferably 1 S / cm or more. Further, it is necessary that the electronic conductivity has a value equal to or higher than those. That is, the mixed conductive oxide targeted by the present invention refers to an oxide whose electronic conductivity and oxygen ion conductivity are both about 0.1 S / cm or more under operating conditions.

As a mixed conductive oxide satisfying this definition
In the old days, JP-A 56-92103 and JP-A 6-92103
As disclosed in JP 1-21717 A, La_x
Sr _1-xCoO_3-aAnd La_1-xSr_xCo_1-yFe_yO_3-zWhen
Oxides having such a perovskite type crystal structure are known.
ing.

More recently, US Pat. No. 5,356,728.
And No. 5580497,
A typical composition is Sr ₄ Fe _6-x Co _x O _z (13−δ ≦ z ≦ 1
3 + δ), and one of the main crystalline phases is a non-perovskite type (Sr ₄ Fe ₆ in the above publication) at least near room temperature.
The same layered perovskite type as the O ₁₃ compound), and has a crystal structure of 10 to 30 S / cm in the atmosphere.
An oxide having an electronic conductivity of about (800 to 950 ° C.) has been invented.

Further, an academic paper by Teraoka et al. (Journal of the Chemical Society of Japan, vol.1988, No.7, pp1084-1089, 1988, "L"
a _1-x Sr _x Co _1-y Fe _y O ₃ oxygen permeation capacity of perovskite type oxide ”), as a result of changing x and y from 0 to 1.0, except for SrCoO _2.5 , x is A composition having a large y and a small y, for example, SrCo _0.8 Fe _0.2 O ₃
In that case, it is described that a good oxygen permeability can be obtained.

[0007] Teraoka et al. Further published the proceedings of the 68th conference of the Institute of Electrochemistry (1J26, pp175, April 1-3, 2001, "Sr,
“Synthesis and oxygen permeability of La—Sr—Co—Fe-based perovskite in the Co-rich composition region”), La at the A site.
Since the oxygen permeability at low temperature is improved by containing
La-Sr-Co-Fe consisting of four components, and Sr
And Co having the highest possible composition, for example La _0.1
It is described that good oxygen permeability can be obtained with a composition of Sr _0.9 Co _0.9 Fe _0.1 O ₃ . In addition, in this composition, SrCo _0.8
Although it is slightly improved in oxygen permeability at 900 ° C. as compared with Fe _0.2 O ₃ , it is reported that it is effective in improving oxygen permeability in a lower temperature region.

[0008]

However, although the composition of the mixed conductive oxide is examined in the above-mentioned prior art documents, the other conditions such as the state of the sintered body and the manufacturing method are industrially applied. Although it is an indispensable technical element when considering, it is hardly described. That is, it has not yet been found under what conditions, when actually applied to a separation membrane for oxygen production or a diaphragm reactor for gas reforming, a sufficiently high oxygen permeability is exhibited. The current situation is that there are none.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an oxygen production method capable of producing oxygen with high efficiency by increasing the oxygen permeability of a separation membrane for oxygen production. And It is another object of the present invention to provide a gas reforming method capable of enhancing the oxygen permeation performance of a diaphragm reactor and performing gas reforming with high efficiency.

[0010]

The present inventors have found that La-Sr-Co-Fe, which has been conventionally considered to have a good oxygen permeability.
As a result of repeated investigations on oxides that have high oxygen permeability when applied to separation membranes for oxygen production or diaphragm reactors, not only the composition of mixed conductive oxides but also sintered bodies It has been found that is required to be more than a certain level. Then, it was found that in order to obtain such a dense sintered body, it is important to control the firing temperature and the temperature during the heat treatment performed prior to firing within a specific range.

The present invention has been made based on such findings, and provides the following (1) to (4).

(1) Mixed conduction having lanthanum, strontium, cobalt and iron as main components, the molar ratio of these component elements being represented by the following formula (1), and having an open porosity of 0.7% or less and being dense. A method for producing oxygen, characterized in that oxygen is produced by using a porous oxide as a separation membrane for producing oxygen. La: Sr: Co: Fe = x: 1-x: 1-y: y (1) (where 0 <x <0.15, 0 <y <0.15)

(2) Obtained by heat-treating a raw material compound containing a metal element at a composition ratio represented by the following formula (1) at a temperature lower than 1100 ° C. to form a mixed oxide, and then firing at a temperature of 1100 ° C. or higher. An oxygen production method comprising producing oxygen by using the mixed conductive oxide as a separation membrane for oxygen production. La: Sr: Co: Fe = x: 1-x: 1-y: y (1) (where 0 <x <0.15, 0 <y <0.15)

(3) Mixed conduction having lanthanum, strontium, cobalt and iron as main components, the molar ratio of the component elements being represented by the following formula (1), and having an open porosity of 0.7% or less and being dense. A gas reforming method comprising reforming a gas by using a porous oxide as a diaphragm reactor. La: Sr: Co: Fe = x: 1-x: 1-y: y (1) (where 0 <x <0.15, 0 <y <0.15)

(4) Obtained by heat-treating a raw material compound containing a metal element at a composition ratio represented by the following formula (1) at a temperature lower than 1100 ° C. to form a mixed oxide and then firing at a temperature of 1100 ° C. or higher. A gas reforming method, characterized in that the mixed conducting oxide is used as a diaphragm reactor to reform a gas. La: Sr: Co: Fe = x: 1-x: 1-y: y (1) (where 0 <x <0.15, 0 <y <0.15)

In the oxygen production method of (2) and the gas reforming method of (4), the mixed conductive oxide film is produced by pulverizing the raw material compound to have a median diameter of 15 μm or less. Preferably there is. Also,
In the oxygen production method of (2) and the gas reforming method of (4), the mixed conductive oxide film is subjected to a heat treatment of 800 to 1000 for converting the raw material compound into a mixed oxide.
It is preferably manufactured by holding at 0.1 ° C. for 0.1 to 30 hours. Furthermore, the above (2)
In the method for producing oxygen and the gas reforming method according to (4) above, the mixed conductive oxide film is produced by pulverizing the mixed oxide after the heat treatment into a median diameter of 10 μm or less and using the mixed oxide. preferable. Furthermore, the above (2)
In the method for producing oxygen and the gas reforming method according to (4), the step of firing the mixed oxide is performed by holding the step of firing the mixed oxide at 1100 to 1300 ° C. for 0.1 to 20 hours. It is preferably manufactured by

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a system diagram showing an outline of an electric power co-production type system capable of implementing the oxygen production method and the gas reforming method according to the present invention.

The raw material air 1 is sent to a pretreatment device 2 to be dedusted and dewatered, and then pressurized by an air compressor 3.
The pressurized compressed air 4 is heated by the heat exchanger 5 and sent to the oxygen production device 7. The temperature-increased air 6 sent to the oxygen production apparatus 7 is provided with a high concentration oxygen 8 and a high concentration nitrogen (exhaust gas) 11 by a separation membrane, which will be described later and is made of a mixed conductive oxide. And separated. The separated high-concentration oxygen 8 is sent to the heat exchanger 9, compressed by the oxygen compressor 10, passed through the booster 12, and then sent to the oxygen consumption equipment 13 such as a smelting reduction furnace, an oxygen blast furnace, and a scrap melting furnace. Be consumed and consumed. Further, the high-concentration oxygen 15 that has passed through the booster 12 and the heat exchanger 9 is sent to a gas reformer 23 having a diaphragm reactor made of a mixed conductive oxide, which will be described later, and a raw material 22 for a reformed gas such as methane is supplied. It is used as a reforming gas. In the gas reforming device 23, the reformed gas raw material 22 is reformed by the high-concentration oxygen 15 to become the reformed gas 24.
5 is discharged to the outside of the gas reformer 23. Oxygen consumption equipment 1
By-product gas 14 such as carbon monoxide and hydrogen generated in 3
The exhaust gas 26 sent to the gas turbine 19 and boosted there is sent to the high-pressure combustor 16, and is burned by a part of the compressed air 4 to drive the gas turbine 17. The driving force of the gas turbines 17 and 19 is transmitted to the air compressor 3 and the oxygen compressor 10 as well as to the gas compressor 20, and the electricity 21 generated in the gas compressor 20 is transmitted to the power generation plant.

The mixed conductive oxide used as the separation membrane of the oxygen production apparatus 7 of FIG. 1 or the diaphragm reactor of the gas reforming apparatus 23 preferably has a film thickness of several tens μm to several hundreds μm. This is because if the film thickness is thinner than this, the strength that can withstand the pressure difference across the film cannot be obtained, and if the film thickness is thicker than this, the oxygen permeation rate is significantly reduced.
In addition, a porous support can be used to reinforce the membrane strength. As a material for the porous support, a material that does not react with the mixed conductive oxide to form a composite metal oxide such as spinel and has a substantially equal thermal expansion coefficient is preferable. The film area of the mixed conductive oxide is appropriately determined depending on the amount of oxygen required, but in order to increase the contact area between the supply gas and the mixed conductive oxide, the mixed conductive oxide surface is made uneven so that the mixed conductive oxide is formed. The area occupied by a product can be reduced. As the film shape of the mixed conductive oxide, there is a flat film or a shell tube structure in which the mixed conductive oxide is formed on the outer surface of the tubular porous support, and the film shape is selected according to the purpose of use. be able to.

Next, an example of the film shape of the mixed conductive oxide used in the oxygen production apparatus 7 will be shown. FIG. 2 is a schematic diagram showing an air separation unit using a mixed conductive oxide as a separation membrane in the oxygen production device 7. Here, an example of a shell tube structure in which a mixed conductive oxide is formed on the outer surface of a tubular porous support is shown. In addition, what is shown here is merely an example, and the film shape is not limited to this.

A Tammann-type tube 30 is installed in the air separation box 29, and the pressurized high temperature raw material air 27 is fed into the air separation box 29 from a raw material air intake port 28 provided in the air separation box 29. ,
Only oxygen 35 permeates from the outer surface of the Tammann type tube 30 to the inside, passes through the oxygen recovery box 33, and is recovered from the oxygen outlet 34. On the other hand, the oxygen-depleted air 32 is discharged from the exhaust gas outlet 31 to the outside of the system.

As shown in FIG. 3 which is a sectional view of the Tammann type tube 30, one end having a thin film mixed conductive oxide 36 on the outer surface of a porous support 37 having continuous through holes is closed. It has a cylindrical shape, and the number and length of the Tammann-type tubes 30 in the air separation box 29 can be changed depending on the intended use. In addition, a support plate or the like can be provided in the air separation box 29 to reinforce the Tammann type tube 30, and the gas flow is controlled in order to efficiently feed the raw material air 27 to the surface of the Tammann type tube 30. It is also possible to provide a rectifying plate for.
Further, the rectifying plate can also serve as the supporting plate.

A plurality of air separation units shown in FIG. 2 can be combined depending on the amount of oxygen produced, the number of air separation units in the oxygen production apparatus is arbitrary, and a Tammann type tube in the air separation box 29 is provided. The number of 30 is also arbitrary.

Next, an example of the film shape of the mixed conductive oxide used in the gas reforming device 23 will be shown. FIG. 4 is a schematic diagram showing a gas reforming unit using a mixed conductive oxide as a diaphragm reactor in the gas reforming apparatus 23. Here, an example of a shell tube structure in which a mixed conductive oxide is formed on the outer surface of a tubular porous support is shown. In addition, what is shown here is merely an example, and the film shape is not limited to this.

The straight tube 44 is installed in the gas reforming box 43, and the reforming raw material gas 38 pressurized from the reforming raw material gas inlet 39 provided in the gas reforming box 43 is used for reforming. Oxygen 42 is fed into the gas reforming box 43 from the oxygen intake 41 via the raw material gas box 40. Then, only oxygen 42 permeates from the outer surface of the straight tube 44 to the inside, and oxidizes the reforming gas 38 fed into the straight tube 44. The oxidized reformed gas 47 is collected in the reformed gas recovery box 45 and recovered from the reformed gas outlet 46. On the other hand, excess oxygen 49 is discharged from the oxygen outlet 48 to the outside of the system.

As shown in FIG. 5 which is a sectional view of the straight type tube 44, both ends having the thin film mixed conductive oxide 50 are opened on the outer surface of the porous support 51 having continuous through holes. It has a cylindrical shape, and the number and length of the straight tubes 44 in the gas reforming box 43 can vary depending on the intended use. Further, in the gas reforming box 43, a support plate or the like can be provided to reinforce the straight type tube 44, and in order to send the oxygen 42 to the surface of the straight type tube 44, the gas flow is controlled. A current plate may be provided. Further, the rectifying plate can also serve as the supporting plate.

A plurality of gas reforming units shown in FIG. 4 can be combined according to the amount of reformed gas, the number of gas reforming units in the gas reforming apparatus is arbitrary, and the gas reforming box 43 is also provided. The number of straight tubes 44 inside is also arbitrary.

Next, the mixed conductive oxide used as the separation membrane for oxygen production and the diaphragm reactor for gas reforming in the above system will be described.

The mixed conductive oxide used in the present invention is
Lanthanum, strontium, cobalt and iron are the main components, the molar ratio of these component elements is represented by the following formula (1), and the open porosity is 0.7% or less. La: Sr: Co: Fe = x: 1-x: 1-y: y (1) (where 0 <x <0.15, 0 <y <0.15)

In such a mixed conductive oxide, the cation is La-Sr-Co-Fe and the chemical formula is ABO.
It is a mixed oxide that can be represented as _X. La and Sr are located at the site represented by A in this chemical formula,
On the other hand, Co and Fe are located at the site represented by B.

When the substitution ratio of Sr by La in the A site is represented by x, 0 <x <0.15. If La is not present, the oxygen transmission rate in the low temperature region of 500 to 900 ° C. is low, but the overall oxygen transmission rate decreases as x increases, so that the above range provides a high oxygen transmission rate. Will be needed.

When the substitution rate of Co in the B site by Fe is represented by y, 0 <y <0.15. If Fe is not present, the symmetry of the crystal structure is lowered, and the presence of Fe is essential because the migration of oxide ions or oxygen vacancies is less likely to occur, but if y is increased to a certain extent or more, the overall oxygen permeability is lowered. Therefore, the above range is required to obtain high oxygen permeability.

The mixed conductive oxide used in the present invention is
Since it is used as a separation membrane for oxygen production and as a membrane reactor for gas reforming, it is necessary to have a high oxygen permeability (selective oxygen transport rate). For that purpose, the composition of the mixed conductive oxide is required. Not only that, it is extremely important to increase the oxygen permeability as a fine microstructure. That is, in the present invention, La-S having the above composition is used.
In the r-Co-Fe mixed conductive oxide, the open porosity should be 0.7% or less. If physical voids are present in the mixed conductive oxide used in the oxygen separation membrane and the membrane reactor, atmospheric gas passing through the voids will be mixed as impurities and the oxygen permeability will be reduced. The open porosity is 0.7 in order to sufficiently suppress the mixing of the impurities.
It is necessary to be less than or equal to%.

By using the mixed conductive oxide having the composition and open porosity defined as described above as a separation membrane for oxygen production or a membrane reactor, a sufficiently high oxygen permeability can be obtained.

Next, a method for producing such a mixed conductive oxide will be described. First, a raw material compound corresponding to the composition of the mixed conductive oxide is prepared. Since the target mixed conductive compound is required to be a single phase, it is advantageous to synthesize it by using an extremely fine solid phase raw material, or a vapor phase or liquid phase compound as a raw material. For example, as shown in the above-mentioned Teraoka et al. Document, nitrates (Fe) and acetates (La, Sr, Co), etc. are used as starting materials for the constituents of the mixed conductive oxide, and the mixture of these is used. It is conceivable to calcine a fine powder obtained from an aqueous solution.

However, in the case of mass production, it is desirable that the raw material itself is inexpensive and the cost in the manufacturing process is also low. With these raw materials, not only the raw material itself is expensive, but also in the manufacturing process. It is also difficult to keep costs low. Specifically, extremely fine solid phase powder not only has a large bulk volume but also easily floats, which requires a large working space and equipment that considers the effects on human health and the surroundings. There is.

In addition, when the liquid phase or gas phase compound is used as the raw material, the above problems are not only the same, but in the case of the liquid phase, equipment and heat supply for removing the solvent are required, If it is a phase, it has a problem that a closed space is required, so that it is difficult to reduce the manufacturing cost.
Further, since the powder is fine, there is a problem that the composition is likely to shift during the calcination and firing steps.

Therefore, in consideration of mass production, it is preferable to obtain the target compound by using a general ceramic raw material. Typical examples of such a raw material include oxides, but carbonates, hydroxides, nitrates, oxalates, sulfates, chlorides and the like may be used in combination.

However, an oxide of an alkaline earth element such as Sr is unstable in the air, and by forming a carbonate or a hydroxide during storage, the content of the metal element in the charged weight is intended. It may deviate from the value. In order to avoid this, it is necessary to carry out a sealing process or a facility that can block carbon dioxide and moisture, but even if these measures are taken, it is necessary to pay attention to artificial negligence.

Since the particle size of the above-mentioned raw material powder is usually about 3 to 30 μm in median diameter, if these are mixed as they are, sufficient component diffusion does not proceed in the calcination treatment,
In addition to the non-uniform composition, formation of coarse higher-order particles by necking may cause problems such as suppressing the density of the compact and not obtaining a dense sintered body. Regarding the non-uniformity of the composition among these, it is possible to eliminate it by raising the calcination temperature or extending the calcination time, but this reduces the density of the sintered body due to the coarsening of the powder, and the production. There is a problem that causes deterioration of sex. For this reason, in order to obtain a powder that is easy to pulverize so that a dense fired body can be obtained while sufficiently diffusing the constituent elements of the target compound, calcination is performed at the lowest temperature and the shortest time possible. In order not to cause inconvenience, it is necessary to make the powder used fine and uniform.

For this purpose, various media mills such as ball mills, attrition mills, and vibration mills can be used without particular limitation as they are usually used. As the mixing and pulverizing method at this time, there are a dry method using only powder and a wet method using water, alcohol, etc., but any method may be used. The particle size of the raw material powder mixture used for calcination is preferably 15 μm or less in median diameter, and more preferably 0.5 to 3 μm.

Heat treatment, that is, calcination is performed prior to the sintering in order to obtain a powder that is easily crushed so that a dense fired body can be obtained while sufficiently diffusing the constituent elements of the target compound. In order to obtain such powder in this calcination, the calcination temperature is important, and for that purpose, the temperature is set to 1
It should be below 100 ° C. Calcination temperature is 1100 ° C
In the above case, the diffusion of the constituents proceeds and the target phase single phase is formed depending on the conditions. In addition to that, the progress of necking formation between the powders makes it possible to perform a dense firing even if it is directly subjected to the steps after molding. In addition to the case where a lump cannot be obtained, the coarse particles that have grown to a diameter of 10 mm or more sometimes have to be crushed prior to the re-grinding, which complicates the process, and the accompanying production. There are problems that lead to an increase in cost and an increase in the amount of impurities mixed.

More preferable calcining conditions are 800 to 100.
Hold at 0 ° C for 0.1 to 30 hours. Calcination condition is 800
If the temperature is less than ℃ and / or less than 0.1 hours, the target phase is not easily generated in the powder after calcination, and if carbonate or hydroxide is used as the raw material compound of the alkaline earth element, the In some cases, decomposition may not be completed, and the effect of calcination may not be sufficiently obtained. On the other hand, if the calcination condition exceeds 1000 ° C. and / or exceeds 30 hours, necking formation between the powders slightly progresses, and the compacts of the sintered body may be slightly inferior when directly subjected to the steps after molding.

Even if the powders are sufficiently mixed and pulverized to diffuse the constituents in the calcination step, and the powders are calcined under appropriate conditions, some of them are partially broken by necking between the powders. Coarse particles of 10 μm are often mixed. It is possible to obtain a dense sintered body by subjecting it to the subsequent steps as it is, but by firing at the lowest possible temperature, and
In order to obtain a dense sintered body with good reproducibility, it is preferable to remove the coarse particles.

It is possible to use a fine filter for removing coarse particles, but in that case, clogging or non-uniformity of components may occur, which is not desirable. In order to avoid such inconvenience, it is preferable to carry out re-grinding in the same manner as mixing and grinding of starting materials. This has the effect of not only avoiding separate equipment investment but also reducing the possibility of impurities being mixed by making production equipment common to other processes. In other words, all processes do not operate every day at the production site in the same way, and especially the operation time of the equipment for the mixing and crushing process is limited. In such a case, another raw material may be processed in a non-operating mixing / grinding facility, and if the subsequent cleaning is incomplete, or if the raw material enters an unexpected location, the cause of contamination of impurities However, by using the equipment for mixing and pulverizing raw materials for mixing and pulverizing after calcination in this way, it is possible to use specific equipment for multiple processes that handle the same raw material, and to prevent the possibility of contamination with impurities. It can be further reduced.

The powder after calcination is molded into a desired shape such as a thin plate or a cylinder by a commonly used molding means such as a doctor blade method, an extrusion molding method, a powder molding method such as uniaxial pressing or isostatic pressing. However, if the powder is too fine, it becomes bulky and inconvenient to handle.Because a large amount of binder component is required, it takes a long time to remove the binder and a dense sintered body can be obtained. There is a problem that cannot be controlled. On the other hand, if the powder to be fired is coarse, it will not be densified, or even if it is densified, it will require a high temperature. Since the mixed conductive oxide according to the present invention contains a transition metal, there is a problem that such a component is diffused into a firing jig at a high temperature, or an alkaline earth metal is volatilized to shift the composition. Considering the above points, the median particle diameter of the powder after calcination is preferably 10 μm or less,
m is more preferred.

The calcined powder that has been re-ground is molded and then calcined to obtain a calcined body. In this case, in order to obtain the dense sintered body of the present invention, the firing temperature needs to be 1100 ° C. or higher. If the upper firing temperature is lower than 1100 ° C., it is substantially difficult to obtain a dense sintered body in a realistic processing time.

More desirable firing conditions are 1100 to 130.
It is to hold at 0 ° C. for 0.1 to 20 hours. 1300
If the temperature exceeds ℃, a dense sintered body can be obtained, but diffusion of transition metals, volatilization of alkaline earth metals and the like are likely to occur, and further, fusion to a firing jig is also unfavorable.

By adopting the above manufacturing method, a dense mixed conductive oxide having the above composition and an open porosity of 0.7% or less can be obtained.

[0050]

EXAMPLES Examples of the present invention will be described below together with comparative examples.

(Example 1) As shown in Table 1, starting materials were La ₂ O ₃ (Kishida chemistry, purity 99.99%), Sr.
CO ₃ (Kanto Kagaku, 99.9%), Co ₂ O ₃ (Kanto Kagaku, purity 99.95%), and Fe ₂ O ₃ (Wako Pure Chemicals, 9
9.9%) to La: Sr: Co: Fe = 1: 9: 9: 1.
Were weighed so that the cation ratio was. Using a wet ball mill, mix these raw materials to the median diameter shown in Table 1.
Crushed. The median diameter is a value measured by using a laser diffraction / scattering particle size distribution measuring device with water as a dispersion medium and sodium hexametaphosphate as a dispersant.

The calcination was carried out in an alumina bowl at 950 ° C. for 10 hours to obtain a perovskite single phase. This powder was finely pulverized again by a wet ball mill to a median diameter shown in the table. The median diameter at this time was also measured in the same manner as the raw material powder.

The finely pulverized powder was dried and then uniaxially pressed and isotropically hydrostatically formed into a disk having a diameter of 15 mm and a thickness of 2 mm. This is baked at 1300 ° C. for 5 hours,
The obtained sintered body was used as an evaluation pellet. The open porosity was measured by the underwater Archimedes method in order to investigate the denseness of the above pellets as a sintered body.

The above pellets had a diameter of about 11 mm and a thickness of about 1
After processing to mm, the ring was fused and fixed to the upper part of the mullite tube by heating to a silver melting point in a tubular furnace using a pure silver ring. Measurement temperature (900 ℃) in this state
To a pellet surface from the upper side of the mullite tube as a raw material gas pure air (mixed gas, O ₂ : 21.05%, N ₂ :
78.95%) was supplied at 20 ml / min. Also,
2 He was used as a purge gas on the surface of the permeated oxygen outlet pellet.
It was supplied at 0 ml / min. Oxygen separated from the raw material air and permeated through the pellets passed through the mullite tube together with the purge gas, and was then subjected to gas chromatography (GC-
TCD), and oxygen permeability was calculated from the detected oxygen. Furthermore, by detecting the N ₂ concentration, the presence or absence of air leakage due to cracking of pellets, defective fusion, etc. was confirmed. At the time of measurement, the measurement temperature was maintained for about 30 minutes, and then the measurement was performed four times at intervals of about 10 minutes. As shown in Table 1, the oxygen transmission rate obtained, about 2.2cm ³ (STP) · cm ^- was high and ² · min ^-1. This value was sufficient for a separation membrane for oxygen production and a diaphragm reactor for gas reforming.

(Example 2) Example 2 except that the calcination conditions were 950 ° C for 1 hour and the firing conditions were 1200 ° C for 5 hours.
Pellets for evaluation were prepared by the same procedure as in 1, and the oxygen permeability was calculated in the same manner. The results are also shown in Table 1. Also in this case, the oxygen transmission rate obtained is about 2.2 cm ³ (ST
P) · cm ⁻² · min ^−1, which was a sufficiently high value as a separation membrane for oxygen production and a membrane reactor for gas reforming.

Example 3 Evaluation pellets were prepared in the same manner as in Example 1 except that the calcination conditions were 850 ° C. for 10 hours and the firing conditions were 1300 ° C.-5 hours. The oxygen permeability was calculated. The results are also shown in Table 1.
Also in this case, the oxygen transmission rate obtained is about 2.1 cm ³ (S
TP) · cm ⁻² · min ^−1, which was a sufficiently high value as a separation membrane for oxygen production and a membrane reactor for gas reforming.

Comparative Example 1 La, Sr, and Co acetates and Fe nitrate were used as starting materials, and these were mixed at the same cation ratio as in the example to evaporate and dry to powder. As a result, calcination is performed at 850 ° C. for 10 hours, and molding is performed in the same manner as in the example to obtain 1100 ° C.
Firing was performed under the condition of 5 hours to obtain pellets for evaluation. Example
Pellets for evaluation were prepared by the same procedure as in 1, and the oxygen permeability was calculated in the same manner. The results are also shown in Table 1. In Comparative Example 1, the open porosity was higher than that of the pellets of the Examples, and the oxygen permeability was accordingly low.

When the fired pellets were left to stand, many of them cracked. Since no particular defects were found on the crack surface, it was speculated that the cause of this was that the strain remaining in the compact due to the use of the fine powder had an effect.

(Comparative Example 2) L which is a constituent of A site
Pellets for evaluation were prepared in the same procedure as in Example 1 except that the a: Sr ratio was changed as shown in the table. As a result, the open porosity was smaller than that of the pellets of Examples 1 to 3. This is because the median diameter of the powder used was made finer than that of the example. However, the oxygen permeability was about 20% lower than that of Examples 1-3. As described above, it was confirmed that even in the case of a dense sintered body, the oxygen permeability is significantly reduced by slightly changing the constituent cation ratio.

(Comparative Example 3) C which is a component of B site
Pellets for evaluation were prepared in the same procedure as in Example 1 except that the o: Fe ratio was changed as shown in the table. As a result, the open porosity was smaller than that of the pellets shown in the examples. This is because the median diameter of the powder used was made finer than that of the example. However, the oxygen permeability was about 20% lower than that of Examples 1-3. As described above, it was confirmed that even with a denser sintered body, the oxygen permeability was significantly reduced by slightly changing the constituent cation ratio.

Comparative Examples 4 to 6 In Comparative Example 4, evaluation pellets were prepared in the same procedure as in Example 1 except that the mixture of starting materials was subjected to the steps after calcination without crushing. No. 5 produced pellets for evaluation by the same procedure as in Example 1 except that the powder after calcination was subjected to the steps after firing without crushing, and in Comparative Example 6, the calcination conditions were 1150 ° C. for 10 hours. Otherwise, the evaluation pellets were produced in the same procedure as in Example 1. As a result, in Comparative Examples 4 to 6, the open porosity in the fired body was large and therefore the oxygen permeability was low, and in Comparative Examples 4 and 6, it was less than half of Examples 1 to 3.
Further, in Comparative Example 5, it was impossible to distinguish between oxygen that passed through the voids of the sintered body and oxygen that diffused in the solid in the amount of oxygen transmitted, and the oxygen permeability could not be measured.

[0062]

[Table 1]

[0063]

As described above, according to the present invention,
Oxygen production and gas reforming are performed with high efficiency by using a mixed conducting oxide having a specific composition and open porosity and high oxygen permeability as a separation membrane and a diaphragm reactor for oxygen production. It can be performed.

[Brief description of drawings]

FIG. 1 is a system diagram showing an outline of an electric power co-production type system capable of implementing an oxygen production method and a gas reforming method according to the present invention.

FIG. 2 is a schematic diagram showing an air separation unit using a mixed conductive oxide as a separation membrane in the oxygen production apparatus of FIG.

FIG. 3 is a sectional view showing a Tammann type tube used in the air separation unit of FIG.

4 is a schematic diagram showing a gas reforming unit using a mixed conductive oxide as a diaphragm reactor in the gas reforming apparatus of FIG.

5 is a sectional view showing a straight tube used in the gas reforming unit of FIG.

[Explanation of symbols]

7: Oxygen production equipment 23; Gas reformer 29; Air separation box 30; Tamman type tube 36, 50; thin film mixed conductive oxide 37,51; Porous support 43; Gas reforming box 44; straight tube

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C01G 49/00 C01G 49/00 A 51/00 51/00 B C04B 35/50 C04B 35/50 (72) Inventor Toshihiko Okada 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan KK (72) Inventor Tatsuro Ariyama 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan KK (72) Invention Kazuya Yabuta 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan KK (72) Inventor Shinichiro Fukushima 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan KK (72) Inventor Koyama Toshiyuki 2-4-2 Daisaku, Sakura-shi, Chiba Taiheiyo Cement Co., Ltd. (72) Inventor Yasutaka Teraoka 1-14 Bunkyo-cho, Nagasaki-shi, Nagasaki Nagasaki University Faculty of Engineering F-term ( Reference) 4D006 GA41 HA24 MA02 MB06 MB19 MC03X NA39 NA51 NA62 PB17 PB18 PB62 PC69 PC71 4G002 AA08 AA09 AA10 AB01 AD02 AD04 AE05 4G040 EA03 EA07 EB11 EB46 4G042 BA30 BA40 4G048 AA05 AB01 AC08 AD01 AE05

Claims (4)

[Claims] 1. A mixed conductivity having lanthanum, strontium, cobalt and iron as main components, the molar ratio of the component elements being represented by the following formula (1), and having an open porosity of 0.7% or less. A method for producing oxygen, comprising producing oxygen using an oxide as a separation membrane for producing oxygen. La: Sr: Co: Fe = x: 1-x: 1-y: y (1) (where 0 <x <0.15, 0 <y <0.15) 2. A material obtained by heat-treating a raw material compound containing a metal element at a composition ratio represented by the following formula (1) at a temperature lower than 1100 ° C. to form a mixed oxide and then firing at a temperature of 1100 ° C. or higher. An oxygen production method comprising producing oxygen using a mixed conductive oxide as a separation membrane for oxygen production. La: Sr: Co: Fe = x: 1-x: 1-y: y (1) (where 0 <x <0.15, 0 <y <0.15) 3. Mixed conductivity having lanthanum, strontium, cobalt and iron as main components, the molar ratio of the component elements being represented by the following formula (1) and having an open porosity of 0.7% or less. A gas reforming method comprising reforming a gas by using an oxide as a diaphragm reactor. La: Sr: Co: Fe = x: 1-x: 1-y: y (1) (where 0 <x <0.15, 0 <y <0.15) 4. A material obtained by heat-treating a raw material compound containing a metal element at a composition ratio represented by the following formula (1) at a temperature lower than 1100 ° C. to form a mixed oxide, and then firing at 1100 ° C. or higher. A gas reforming method comprising reforming a gas by using a mixed conductive oxide as a diaphragm reactor. La: Sr: Co: Fe = x: 1-x: 1-y: y (1) (where 0 <x <0.15, 0 <y <0.15)